Well, he did bring it up already which says to me he is already amenable to changing it. That is already a huge hurdle out of the way! My concern of course is that at this point he may be outside a return period and if you do not have a trade in policy, it will not be as easy to do (if too late for you, maybe others can heed the advice of speaking up earlier). So, you may have to suck up extra costs if you decide to go ahead. To me sharing the cost is a no-brainer. If you are getting married, ultimately it is all coming from the same place anyway. Paying more now from either pocket is less money later together. Just the way it works. You may already live together or share finances anyway, so again, a no-brainer.
Not all men are that sentimental about the ring itself as an object. People can remain sentimental about the meaning, and the experience, and not need the ring to give them that. My own husband sees whatever rings we wear more as a symbol to honour our commitment, and not the actual relationship itself, as do I. Rings can be damaged, lost, stolen, outgrown, cause allergic reactions or discomfort, worn down and so on. You NEVER know what will happen to the ring. I never had an engagement ring originally, but we did look, and even then my husband talked about maybe on a special trip in a couple years or so we could upgrade.
I did, however, change my original wedding band, the one we exchanged at our ceremony. Partly due to allergies but mostly due to style and comfort issues, and all I did was be honest with him and let him know what I was not happy about. At first he was a little sad and surprised, but we talked openly and honestly with each other, and it turned out I was making a far bigger deal out of it than he ever did. He was thankful I talked to him and let him know, rather than pretend to love it, though he did tease me for a while about it (saying “ick” in a dramatic funny way when he looked at my ring on my finger or talking about how much he LOVED his ring…sometimes he still does tease me, but it is all in good humour and we really do laugh about it). We decided to get new rings (out of shared finances of course!). When I had allergies and issues with my SECOND set, I did the same thing (along with promised no more changes unless it was to a twist tie!) and he was actually happy as he did not like that set much anyway. Ultimately, he wanted me to wear something I loved as much as HE loved his own ring (he adores his). Why would he want me to wear something I did not feel joy and pride in wearing? Fortunately now we BOTH love love love my rings. He is often telling me how much he likes them and shows them off to others (even though I was the one who picked them out entirely!). They are perfect for me and my forever set.
You know your partner, and relationship, better than we do. In my own relationship, we have a commitment to honesty and being authentic with one another. If something is on our mind, we talk. If someone wants to talk, we listen. We are each responsible for our selves and putting what we need and want out there. We are not mind readers. We also accept responsibility for our emotions. If my husband was hurt by me wanting to change my ring, it was his responsibility to communicate that to me, and we could address that together, not for me to tip toe around and not say anything and remain upset myself to spare him. He would not want that either! We are in this as a team, and if something is bothering one of us we are committed to working together on it. While a ring may seem “insignificant” in the grand scheme of things, if it bothers you and you are staying quiet instead of talking about it, and developing negative associations around it, then it IS significant. So talk about it!
You could make a new experience together, one where you choose the stone out yourself as a couple and have new memories.